The present invention relates to steganography, digital watermarking and security enhancements.
Digital watermarking is a form of steganography that encompasses a great variety of techniques by which plural bits of digital data are hidden in some other object without leaving human-apparent evidence of alteration.
Digital watermarking may be used to modify media content to embed a message or machine-readable code into the content. The content may be modified such that the embedded code is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process.
Most commonly, digital watermarking is applied to media such as images, audio signals, and video signals. However, it may also be applied to other types of data, including documents (e.g., through line, word or character shifting, through texturing, graphics, or backgrounds, etc.), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems typically have two primary components: an embedding component that embeds the watermark in the media content, and a reading component that detects and reads the embedded watermark. The embedding component embeds a watermark by altering data samples of the media content (e.g., pixel values, DCT coefficients, wavelet coefficients, etc). The reading component analyzes content to detect whether a watermark is present. In applications where the watermark encodes information, the reading component extracts this information from the detected watermark. Commonly assigned U.S. Pat. Nos. 6,614,914 and 5,862,260 discloses various encoding and decoding techniques.
Some aspects of the invention relate to inconspicuously embedding binary data in line art images (such as are used in currency, graphics, identification documents and the like), and associated methods/systems for decoding such data from such images. Other aspects of the invention relate to security features and confidence clues for identification documents, currency, graphics and the like. Still other aspects of the invention provide related systems and methods.
In the following disclosure it should be understood that references to watermarking encompass not only the assignee's watermarking technology, but can likewise be practiced with any other watermarking technology.
Some of the prior art in image watermarking has focused on pixelated imagery (e.g. bit-mapped images, JPEG/MPEG imagery, VGA/SVGA display devices, etc.). In some watermarking techniques, the luminance or color values of component pixels are slightly changed to effect subliminal encoding of binary data through the image. (This encoding can be done directly in the pixel domain, or in another domain, such as the DCT domain.) In some systems, isolated pixels are changed in accordance with one or more bits of the binary data; in others, plural domain-related groupings of pixels (e.g. locally adjoining, or corresponding to a given DCT component) are so changed. In all cases, however, pixels have served as the ultimate carriers of the embedded data.
One inventive technique for authentication and copy detection employs ink pairs to provide authentication clues for security documents (e.g., banknotes, currency, checks, financial instruments, etc.) and identification documents (e.g., driver's license, passport, visa, ID card, bank cards, etc.). An ink pair cooperates to provide a diffraction grating (or other reflective pattern) while obscuring the location of a metallic ink—one of two inks in an ink pair.
According to one aspect, a document includes a first surface and a second surface. The first surface comprises a first set of print structures and a second set of print structures. The first set of print structures and the second set of print structures cooperate to obscure the location on the first surface of the second set of print structures. The second set of print structures is arranged on the first surface so as to provide a reflective pattern.
In a related example, the reflective pattern forms a diffraction grating.
In another related example, the first set of print structures is provided on the first surface with a first ink and the second set of print structures is provided on the first surface with a second different ink. The second different ink is a metallic ink.
In still another related example, the first set of print structures and the second set of print structures collective convey a steganographic signal (e.g., a digital watermark) that is discernable from optical scan data representing at least a first portion of the first surface.
According to another aspect of the invention, a photo identification document includes a first surface and a second surface. The second surface includes a photographic representation (e.g., a picture or photo) of an authorized bearer of the photo identification document. The first surface comprises a first set of print structures provided thereon with a first ink having a first color and a second set of print structures provided thereon with a second ink having a second color. The first color and the second color are visually similar colors. The first set of print structures and the second set of print structures cooperate to obscure the location on the first surface of the second set of print structures. The second ink comprises metallic characteristics so when arranged on the first surface, the second set of print structures provide a diffraction grating.
According to still another aspect of the invention, a security document (e.g., a banknote, check, note, draft, etc.) includes a first surface; a first set of print structures provided on the first surface with a first ink having a first color; and a second set of print structures provided on the first surface with a second ink having a second color. The first color and the second color are visually similar colors. The first set of print structures and the second set of print structures cooperate to obscure the location on the first surface of the second set of print structures. The second ink comprises metallic characteristics so when arranged on the first surface, the second set of print structures provide a pattern that, in response to a signal or radiation, reflects a predetermined signal or pattern.
The foregoing features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.